1. Field of the Invention
The present invention relates to a metal gasket for sealing between confronting surfaces of the cylinder block and the cylinder head in the engine and, more particularly, to the metal gasket composed of carrier plate with beads thereon and a stopper plate with folded constructions thereon.
2. Description of the Prior Art
Conventionally, the metal gaskets have been widely applied to the engines in sealing between a cast-iron cylinder block, which is less in both of wall thickness and weight, and an aluminum cylinder head of less weight and also in sealing between the aluminum-made block and head. In prior metal gaskets of various types, a metal gasket has been well known to those skilled in the art, which includes a stopper plate having folded constructions to help ensure what is referred as xe2x80x9ccompression stopper functionxe2x80x9d, which protects a bead carrier plate from a permanent set or flattering out owing to the excessive compressive loading or stress. The exemplary metal gaskets having the compression stopper function are disclosed in Japanese Utility Model Laid-Open Nos. 170053/1985; 118147/1989; 118148/1989; 134761/1989 and Japanese Patent Laid-Open Nos. 255253/1986; 101575/1988 and 15372/1992. Although the folded constructions in the prior metal gaskets disclosed in the above citations have for their objects to achieve the functions or effects of compression stopper as well as air-tight sealing, there has been heretofore disclosed no concept or consideration as to what change happens at a gap in the folded construction during engine operation, or how relationship is present between the degree or effect of the gap and the structure or material of the engines.
Experimental data required for the design of metal gasket have been commonly obtained by measuring the deformation in the cylinder head when the cylinder bores have been repeatedly compressed and decompressed, on the assumption that the cylinder block may be considered an absolute or ideal rigid body and, therefore, only the cylinder head is subject to the deformation due to the engine operation. As an alternative prior art to gain the data for the metal gasket design, the thermal deformation of the cylinder head has been measured, which takes place when the cylinder head is heated up to a high temperature.
Nevertheless, the prior experimental data heretofore prevailed for the design of metal gasket, whether it depends on variation in pressure or in temperature, belongs to the data as to the static deformation and, therefore, fails in measuring the simulation of the phenomenon, which may come into action in the metal gasket, accompanied with the deformation which might occur in the cylinder block when the metal gasket is squeezed interposed between the mating cylinder block and head, the permanent distortion which might exerted on the cylinder block owing to undue thermal stress or fatigue as a result of the engine operation, and the intolerable clearance caused between the gasket and the cylinder block by the distortion in the cylinder block or head. That is to say, any prior experience for the design of the metal gasket has provided no data representing the true behavior on the deformation of the metal gasket, which fairly reflects the operating conditions of the engine. Moreover, the state of the art in metal gaskets has recently progressed in the theoretical analysis technique on an aspect of dynamics of structure in accordance with the finite-element method, whereas there is scarcely any experimental data about the behavior of the metal gasket, which is in compliance with the behavior of the distortion occurring in the cylinder head under the test of actual engine performance. Thus, such prior state of the art in metal gaskets has been quite insufficient to design and produce the metal gaskets rich in reliability.
Referring to FIG. 19 in which a conventional metal gasket is shown placed between confronting surfaces of a cylinder head 20 and a cylinder block 21, which are made of either aluminum alloy or thin cast iron, the metal gasket is composed of a pair of carrier plates 22, 24 having thereon with corrugations, or beads, not shown, and a stopper plate 23 partially folded back so as to have flanges 25 that are made in face-to-face close engagement with any one surface of the major portion of the stopper plate 23. When squeezing or tightening the metal gasket constructed as described above between the mating surfaces of the cylinder head 20 and the cylinder block 21, the cylinder block 21 is often rendered deformed at 36, or at peripheral edges around cylinder bores in the cylinder block 21, which may results from either the thermal stress or the fatigue owing to the engine operation. This causes the permanent set or permanent strain in the associated carrier plate 24 of the metal gasket, resulting in causing intolerable clearances 36S between the associated plates of the metal gasket. Thus, the metal gasket is made inferior in sealing performance and, in some cases, damaged by cracks or the like, which may be caused at beads formed on the carrier plates 22, 24. It will be noted that the cause of the problem involved in the prior metal gasket is somewhat exaggerated in schematic view of FIG. 19.
The major sources of the damages occurring in the prior metal gaskets may be considered as follows. In the stopper plate incorporated in the prior metal gasket, in which the folded flanges are made in face-to-face close contact with the major portion of the stopper plate around the entire periphery of the cylinder bores, the folded constructions are designed so as to become relatively higher in strength, so that they remain in substantially horizontal state they have been placed on the deck surface of the cylinder block, even under the thermal stress during the engine operation. Thus, the folded constructions may not help compensate for undue clearances that might happen between the bottom surface of the metal gasket and the mating deck surface around the peripheral edges of the cylinder bores. It would seem most fitting that such undue clearances grow into permanent set or permanent distortion in the bead carrier plates, resulting in the occurrence of intolerable clearances either between any adjoining metal plates or between the cylinder block and its associated bead carrier plate. Moreover, in case where the intolerable clearances occurring in the metal gasket result in increasing excessively the intervals of gaps in the folded constructions of the stopper plate and also the strength of the folded constructions is too inadequate for compensating for the intolerable clearances, a serious problem arises in which the engine operation as in starting the engine causes repeatedly a vicious spiral of premature loss of the gaps, permanent set in fatigue of the beads, reduction in compressive force of the tightening bolts, increase in distortion of the cylinder head and propagation of the permanent set, thus resulting in making it much more difficult to compensate for the changes of the clearances between the cylinder block and the head. This causes cracks at the beads of the carrier plates, which are thus subject to the corrosion at the beads by the gases leaking out of the cracked beads with the result of the failure in sealing performance of the metal gaskets. The problem described just above will become increasingly critical under any situation where the compressive forces of the tightening bolts are considered less or the counter-bores are less in depth.
In a metal gasket a stopper plate is partially folded back to thereby form the folded constructions for providing the compression stopper function, the folded constructions are simply twice as thick as the stopper plate. The folded constructions of twice thicker than the stopper plate itself, in some cases, are too sufficient for the compressive stopper function, instead, may cause sometimes the stress concentration of the compressive surface-to-surface pressure at the areas around the cylinder bores. Such concentration of the compressive surface-to-surface pressure occurring in the folded constructions makes worse the uniformity of the compressive surface-to-surface pressure over the entire mating surfaces of the metal gasket, namely, makes unbalance of the compressive stress between at the areas around the cylinder bores and at the other residual area, for example, around openings for cooling water or oil. A consequent problem may arise in the sealing performance around the openings for water or oil. Moreover, the stopper plate of the type described above has the disadvantages of causing the cracks owing to undue the stress concentration at the folded constructions, especially, at the bents of the folded flanges for defining the cylinder bores, and also of not providing sufficient elastic deformation to the beads of the carrier plates thereby failing in forming the reliable annular face-to-face contact areas.
Most stopper plates are by nature to protect the beads on the carrier plates from the permanent set or flattening out when the metal gasket is squeezed by the action of the tightening force. In the stopper plate in which positive stoppers are provided by partially folding back a metal plate, each folded construction should have an amount of gap of at most about 10 xcexcm in order to helpensure the amount of compression stop kept uniform around the associated cylinder bore. In contrast, even if the amount of gap at the folded construction exceeds about 10 xcexcm, there is a danger that the folded construction is lost on the compression stopper function. As will be understood from the foregoing description, it will be thus anticipated to develop a metal gasket protected from the failure of sealing performance owing to the inadequate gaps at the folded constructions and the consequent permanent set in fatigue of the beads. Moreover, the metal gasket ought to cope with the intolerable clearances that might occur between the mating surfaces of the metal gasket and the cylinder block around the periphery of the cylinder bores. More particular, it is expected to resist against the decline in sealing performance and the unanticipated cracks, which might otherwise occur at the beads due to the increase of the intolerable clearances caused by the folded constructions lacking of compensation for the intolerable clearances, and also protect the beads against the corrosion resulting from the combustion gases leaking out of the intolerable clearances.
The present invention has for its primary object to provide an improvement in a metal gasket suitable for engines of structures or materials compelled to admit less squeezing force of head bolts, for example, an engine having more than six cylinders, in which it is very hard to keep a compressive stress due to squeezing force uniform throughout the entire surfaces of the metal gasket. More particularly, the primary object of the present invention is to provide an improved metal gasket ensuring the sealing function for the mating surfaces of the cylinder block and the head, and further ensuring the compressive beads against damage, thereby resulting in helping ensure the long service life. To this end, the improved metal gasket of the present invention is comprised of carrier plates with compressive beads thereon, and a stopper plate arranged in an overlapping relation with the carrier plates and provided integrally with folded constructions, where folded flanges are kept spaced due to the elasticity away from the confronting surface of the stopper plate even during the engine operation whereby the folded constructions elastically compensate for intolerable clearances occurring between the metal gasket and cylinder block.
The present invention is concerned with a metal gasket comprising at least one carrier plate of an elastic metal plate adapted to be used interposed between a cylinder block and a cylinder head to be fixed to the cylinder block, the carrier plate being provided with first bore openings and beads that are each developed along the associated first bore opening, and a stopper plate of an elastic metal plate overlaid on the carrier plate, the stopper plate being partially folded back thereby providing annular folded constructions to define second bore openings in alignment with the first bore openings, wherein the beads on the carrier plate are overlaid on the stopper plate at areas spaced apart from the folded constructions which are each composed of a folded flange area and its counterpart area extending along a perimeter of the associated second bore opening, and the folded constructions each include a gap of a preselected interval between the folded flange area and its counterpart area to provide elasticity at the folded construction continuously whenever the gasket is loaded inclusive of under engine operation.
The stopper plate is to protect the compressive beads on the carrier plates against permanent set or flattening out when squeezed by the head bolts, and also to compensate elastically for the intolerable clearances that might occur in the cylinder block. Moreover, with the stopper plate being overlaid to the carrier plates, the folded constructions of the stopper plate are kept apart away from the beads on the carrier plates continuously with no relation to whether the gasket is in any one of released event, squeezed event and engine operation.
According to one aspect of the present invention, a metal gasket is provided wherein the stopper plate is overlaid on the carrier plate such that raised surfaces of the beads on the carrier plate make abutment against a major flat surface of the stopper plate while the beads are spaced apart from perimetric edges of the folded flange areas of the folded constructions in the stopper plate. Moreover, the stopper plate may be arranged interposed between the confronting carrier plates with beads in such a manner that the raised surfaces of the beads on the carrier plates make abutment against the major flat surface of the stopper plate. As an alternative, the stopper plate may be overlaid on the carrier plate such that recessed surfaces of the beads confront a major flat surface of the stopper plate while perimetric edges around the first bore openings in the carrier plate are spaced apart from the perimetric edges of the folded flange areas of the folded constructions on the stopper plate.
In another aspect of the present invention a metal gasket is provided wherein the stopper plate is used in such arrangement that the folded flange areas in the folded constructions make contact with the cylinder block whereby the elasticity exerted by the folded flange areas compensates for intolerable clearance, or distortion, occurring in the cylinder block. The gaps between the folded flange areas and the counterpart areas are adequately kept even under such event that the gasket is subjected to the squeezing or tightening load. The gaps provided between the confronting folded flange areas and the counterpart areas are preset to hold the range of from 20 xcexcm to 200 xcexcm in the released event. In addition, an amount of compression stop anticipated by the folded constructions is preselected in a range of from 100 xcexcm to 360 xcexcm in a released event. Furthermore, a compressive surface-to-surface pressure at the folded constructions on the stopper plate is preselected in a range of from 70 MPa to 140 MPa while a compressive surface-to-surface pressure at the beads on the carrier plate is preselected in a range of from 10 MPa to 110 MPa.
In another aspect of the present invention a metal gasket is provided wherein the folded constructions of the stopper plate are each regulated in its width along circumferences of the associated second bore opening in such a manner that it is made less at zones including a plane spanning across centers of any adjoining second bore openings, while made greater at other residual zones. Moreover, while the gaps provided between the folded flange areas and their counterpart areas are regulated in intervals so as to differ for each of the juxtaposed second bore openings, the folded constructions are also regulated in widths so as to differ for each of the juxtaposed second bore openings.
In a further another aspect of the present invention a metal gasket is provided wherein the folded constructions are formed by partly folding back thin areas of the stopper plate into folded flange areas, which are reduced in thickness, compared with a major portion of the stopper plate, to an extent more than half the major portion. Moreover, an amount of compression stop to control the degree of compression exerted on the beads comes into action due to the difference in thickness between the folded construction and the major portion of the stopper plate and, therefore, the amount of compression stop is regulated in accordance with the thickness of the thin areas that is reduced, compared with the major portion. The compression stopper function arising in the stopper plate of the present invention may be relieved compared with that of the stopper plate in which the stopper constructions are formed by only doubling over a simple stopper plate uniform in thickness. According to the present invention, since the thin areas of the stopper plate are reduced down to a thickness more than half the residual major potion of the stopper plate, doubling the thin area into two, namely, the folded flange area and the counterpart area, results in providing a folded construction, or stopper construction, which is made greater in total thickness than the major portion, but less than twice the major portion.
The stopper plate of the present invention causes no excessive concentration of the compressive surface-to-surface pressure at the folded constructions when the metal gasket is squeezed between the mating surfaces of the cylinder block and head. At the same time, the beads on the carrier plates are subjected to an adequate compressive deformation, thereby providing annular elastic contacting areas sufficient to help ensure satisfactory sealing performance.
In another aspect of the present invention, a folded construction is provided wherein confronting surfaces of the folded flange area and the counter area are partially or substantially throughout coated with elastic material. Coating the elastic material on the surfaces defining the gap in the folded construction provides the cushioning performance to help keep the spring action even in the event the gap is made reduced under compressive loading. Consequently, a minimum spring action or stopper function may be ensured with no permanent set or deformation in fatigue even in the areas other than the compression side of the sharp bent at the folded construction. According to another aspect of the present invention, a composite material containing aluminum and chlorine is applied to the compression side at the sharp bent in the folded construction, where a penetration layer of aluminum is built up on the applied surface of the compression side by thermal diffusion of aluminum during the engine operation. The diffusion-penetration layer built in the compression side at the sharp bent contributes to the protection of the sharp bent in the folded construction against the deterioration in strength, thereby reducing or substantially eliminating the permanent set of deformation in fatigue at the sharp bent. The amount of compression stop to control the degree of compression exerted on the beads comes into action due to the difference in thickness between the folded construction and the major portion of the stopper plate and, therefore, the amount of compression stop is regulated, depending on the thickness of the thin areas, which is reduced compared with the major portion of the stopper plate.
In accordance with the metal gasket constructed as described just above, the folded constructions of the stopper plate may not only develop an adequate compressive surface-to-surface pressure, but also regulate the amount of compression stop for the beads on the carrier plates. The folded constructions assure the gaps thereof the elasticity to keep the gaps at an adequate situation regardless of compressive stress due to not only squeezing force of head bolts but also engine operation. The elasticity at the folded construction forces the gaps into expanding to compensate for the intolerable clearances that might take place owing to the permanent distortion occurring in the cylinder block or head around the cylinder bores. That is to say, the gaps in the folded constructions may undergo change in intervals, following the increase of the clearances between any mating surfaces, to make up for the intolerable clearances, thereby keeping the compressive surface-to-surface pressure at an adequate pressure level for a long service life. This makes it possible to eliminate the occurrence of unanticipated clearances between any adjoining overlaid metal plates, thus protecting the metal plates against the leakage of gases into between the metal plates with result of maintaining the sealing performance.
In the metal gasket of the present invention, the gaps in the folded construction are designed to continue to keep the acting action, stopper effect and sealing performance at their minimum requisitions. The gaps provided in the folded constructions are regulated properly in the released event before squeezing by head bolts and also hold the confronting surfaces of the folded constructions, spanning across the gaps, at an elastic relation such that the confronting surfaces make scarcely engagement throughout with each other even under the engine operation. The elasticity to keep the gaps regardless of compressive load is in particular provided at the compression side of the sharp bent in the folded construction. Furthermore, the stopper plate is used in such arrangement that the folded flange areas in the folded constructions make contact with the cylinder block whereby the elasticity exerted by the folded flange areas compensates for the intolerable clearances that might happen, in particular, due to the distortion occurring in the cylinder block.
Although the gaps in the folded constructions becomes narrower gradually with the lapse of time during which the engine operates, the gaps are set such that they are kept from being completely crushed or collapsed. The regulation of the gaps in the folded constructions at the released event prior to squeezing by the head bolts must be carried out with having considered that the gaps in the folded constructions are compressed much at the initial squeezing and thus made less in intervals at areas neighboring the head bolts, compared with the intervals at the other areas. Thus, the metal gasket may be not only protected against the leakage of combustion gases and enhanced in the stopper effect, but also prevented from the permanent set or deformation in fatigue of the gaps in the folded constructions.
When the distortion around the cylinder bores in the cylinder block becomes too large, the distortion results in increasing the intolerable clearances between the bottom surfaces of the metal gasket and the upper surface of the cylinder block at the areas neighboring the perimetric edges of the cylinder bores, or between mating surfaces of the folded constructions and the cylinder block. Nonetheless, the gaps in the folded constructions, in particular, at the compression sides of the sharp bents, are kept at a constant interval. In the released event prior to the squeezing of head bolts, the gaps at the compression sides in the folded constructions are not formed in a circle, but in a shape of U or raindrop turned sidewise, so that they may be kept at a somewhat compressed raindrop-shape to resist against the collapse or crush. Thus, the gaps at the compression sides make downward deformation, following the increase of the intolerable clearances caused by the distortion in the cylinder block, thereby compensating for the intolerable clearances to help ensure both the stopper effect and the sealing performance.
Compensating for the intolerable clearances with the folded constructions results in keeping the metal gasket from the invasion of the combustion gases and also protecting the cylinder head against the distortion. Consequently, the carrier plates with the beads thereon and the stopper plate with the folded constructions thereon are both made less in the behavior of deformation whereby the beads may be protected against crack. It is thus critical that the gaps in the folded constructions, preselected properly in the released event before squeezing the head bolt, must be so regulated as to be kept at an efficient interval even in the engine operation.
If either the deterioration in sealing performance or the crack in beads may be eliminated by only the common regulation to the gaps in the folded constructions, the regulation of the gaps in the released event before squeezing should be individually calibrated for every cylinder bore opening corresponding to each cylinder bore. Moreover, the gaps in the folded constructions may each varied in interval along the circumference of the associated cylinder bore opening. Distribution of a desired compressive surface-to-surface pressure around the cylinder bore openings is obtained by regulating conditions as to the gaps, doubled widths of the folded constructions in the released event along the circumference of the associated cylinder bore opening. Moreover, the distribution of the desired compressive surface-to-surface pressure may be found by calibrating the conditions as to the gaps, doubled widths, amounts of compressive stop or shoulder of the folded constructions, which have been given in the released event, along the circumference of the associated cylinder bore opening corresponding to each cylinder bore, in compliance with a distribution of distortion in the cylinder bores, which is actually measured during the engine operates. To cope with large intolerable clearances, the distribution of the compressive surface-to-surface pressure is adjusted in such a manner as to place weight on the stopper areas than on the bead areas. The application of large compressive stress onto the bead areas at the start of squeezing raises the permanent deformation of the folded flange areas in the folded constructions, which causes the premature permanent set or fattening out in fatigue of the beads, thereby resulting in rapid deterioration of the sealing performance. Accordingly, it is preferred to carry out the simultaneous regulation or calibration of the beads in width and height.
For continuing to keep the sealing performance for the acceptable service life, it is preferred to make any width of the folded construction less at an area between any two adjoining bore openings, but increased at areas much subjected to distortion of the cylinder head, provided if the flange areas are folded back on the side of the cylinder block. Moreover, the regulation on the folded constructions and the beads along the circumference of the associated bore opening may be made common to the cylinder bore openings.
In the metal gasket of the present invention constructed as described just above, the folded constructions having the gaps may well follow the changes of the intolerable clearances, occurring around the cylinder bores in the cylinder block, by the elastic action of the gaps to thereby compensate for the intolerable clearances with the folded constructions, thus keeping the areas around the cylinder bores at an adequate compressive surface-to-surface pressure and ensuring good sealing performance.
Other objects and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.